Can’t ping my XP machines

I have two XP machines at home wired into a Linksys WRT54G router. Wireless is fine. Internet access is fine. But the two boxes wired into the back of it cannot see each other. Both are running XP home. All firewalls are off. All TCP/IP looks fine. I even reached a point where I could ping the one machine and have Zonealarm block the request. Turned off Zonealarm, still no go. Windows firewalls are turned off. I would delete the TCP/IP and reinstall, but you cannot delete TCP/IP from XP. Any ideas? Thanks.